Hydrocarbon retaining and purging system for flex-fuel combustion engine

ABSTRACT

Systems, methods, and computer readable storage media are described in which exhaust gas is routed to a hydrocarbon retaining device during starting, and purged to the engine intake manifold. Various alternative approaches are described for controlling operation and diagnosing degradation. Further, various interrelated configurations are described.

The present application claims priority to provisional application60/987,350, filed Nov. 12, 2007, the entire contents of which areincorporated herein by reference for all purposes.

FIELD

The present description relates generally to an exhaust treatment systemfor a combustion engine.

BACKGROUND/SUMMARY

Engine exhaust systems have utilized hydrocarbon retaining devices, suchas hydrocarbon traps, to retain cold start emissions for later reaction,or to recirculate into the engine intake system. In one particularexample, the purging of exhaust gases may be enabled when the devicereaches a predetermined temperature.

However, the inventors herein have recognized several issues with suchexamples. Specifically, the engine may operate with varying fuelcompositions thereby producing exhaust emissions that may have differentadsorption and/or desorption characteristics. For example, flex-fuelvehicles that operate on fuel having a varying alcohol composition(e.g., ranging from gasoline (E0) to ethanol (E85)) may havesignificantly different exhaust water content, thereby affecting thetemperature at which exhaust constituents are stored and/or released.Further, different hydrocarbon chains may be produced in the exhaustdepending on the fuel composition also having different storage/releasecharacteristics. In one particular example, hydrocarbons may be trappedin an HC retaining device up to higher temperatures with increasedalcohol content in the fuel. As such, an appropriate control to trappingtailored for combustion of one fuel composition may lead tobreakthrough, or inefficient trapping, for combustion of a second fuelcomposition.

The above issues may be addressed by a method of operating an enginehaving an intake, an exhaust, and a hydrocarbon-retaining system, theengine combusting fuel, the method comprising: selectively routingexhaust gases of the engine to the hydrocarbon retaining system to storeexhaust hydrocarbons; selectively purging stored hydrocarbons from thehydrocarbon retaining system to the engine intake; and varying aninitiating of the selective purging of stored hydrocarbons responsive toa condition.

In one example, the purging can be adjusted to the particular fuelproperties of the fuel combusted in the engine, such as the alcoholcontent of the fuel combusted in the engine. In this way, it is possibleto adjust the purging to take advantage of the particularstorage/release properties of the exhaust constituents particular to thecombusted fuel alcohol content. This can increase the storage capacityutilization, as well as reduce breakthrough of the hydrocarbon-retainingsystem.

It should be understood that the summary above is provided to introducein simplified form a selection of concepts that are further described inthe detailed description. It is not meant to identify key or essentialfeatures of the claimed subject matter, the scope of which is defineduniquely by the claims that follow the detailed description.Furthermore, the claimed subject matter is not limited toimplementations that solve any disadvantages noted above or in any partof this disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a schematic depiction of an engine, exhaust system, and ahydrocarbon (HC) retaining system.

FIG. 2 shows a schematic depiction of an internal combustion engine.

FIGS. 3, 4, 5, 6, and 7 show various embodiments of the HC RetainingSystem.

FIGS. 8, 9, 10, 11, 12, 13, and 14 show high level flow chartsillustrating operation of the engine, exhaust system, as well as the HCRetaining System.

DETAILED DESCRIPTION

FIG. 1 shows a schematic depiction of a vehicle system 6. The vehiclesystem 6 includes an engine system 8 coupled to a hydrocarbon (HC)retaining system 22 and a fuel system 18.

The engine system 8 may include an engine 10 having a plurality ofcylinders 30. The engine 10 includes an intake 23 and an exhaust 25. Theintake 23 includes a throttle 62 fluidly coupled to the engine intakemanifold 44 via an intake passage 42. The exhaust 25 includes an exhaustmanifold 48 leading to an exhaust passage 35 that routes exhaust gas tothe atmosphere. The exhaust 25 may include one or more emission controldevices 70, which may be mounted in a close-coupled position in theexhaust. One or more emission control devices may include a three-waycatalyst, lean NOx trap, diesel particulate filter, oxidation catalyst,etc. It can be appreciated that other components may be included in theengine such as a variety of valves and sensors, shown in the exampleengine of FIG. 2.

The exhaust 25 may also be operatively coupled to hydrocarbon retainingsystem 22 via conduit 26 and valve 24. In one example, exhaust gases maybe routed to the hydrocarbon retaining system 22 during engine coldstart operation. Then, once the emission control device 70 has reachedits operating temperature, the hydrocarbons retained in system 22 may bepurged to the engine via intake 23, as described below herein.

Returning to FIG. 1, fuel system 18 may include a fuel tank 20 coupledto a fuel pump system 21. The fuel pump system 21 may include one ormore pumps for pressurizing fuel delivered to the injectors of engine10, such as the example injector 66 shown. While only a single injector66 is shown, additional injectors are provided for each cylinder. It canbe appreciated that fuel system 18 may be a returnless fuel system, areturn fuel system, or various other types of fuel system. Vaporsgenerated in the fuel system 18 may be routed to hydrocarbon retainingsystem 22, described further below, via conduit 31, before being purgedto the engine intake 23.

The fuel tank 20 may hold a plurality of fuel blends, including fuelwith a range of alcohol concentrations, such as various gasoline-ethanolblends, including E10, E85, gasoline, etc., and combinations thereof.

Hydrocarbon retaining system 22 may include one or more hydrocarbonretaining devices, such as a hydrocarbon trap configured to temporarilytrap hydrocarbons from entering gases. Hydrocarbon retaining system 22may further include a vent 27 which may route gases out of the retainingsystem 22 to atmosphere when storing, or trapping, hydrocarbons from theexhaust 25 and/or fuel system 18. Vent 27 may also allow fresh air to bedrawn into hydrocarbon retaining system 22 when purging storedhydrocarbons from the exhaust 25 and/or fuel system 18 to the intake 23via purge conduit 28 and purge valve 29. While this example shows vent27 communicated with fresh, unheated air, various modifications may alsobe used. For example, heated intake air from an air cleaner box may beused. Further, heated exhaust gas may be used under selected conditions.

Various system configurations of hydrocarbon retaining system 22 insystem 6 may be used, with various combinations of valves, sensors, andthe like. For example, various system configurations are describedherein with regard to FIGS. 3-7, discussed below. And while the variousconfigurations of FIGS. 3-7 show various alternative features inparticular combinations, the various features from among FIGS. 3-7 mayalso be combined together to form still further example configurations.Further various additional components may be included in the intake,exhaust, and fuel system, such as a muffler downstream of valve 24.

The vehicle system 6 may further include control system 14. Controlsystem 14 is shown receiving information from a plurality of sensors 16(various examples of which are described herein) and sending controlsignals to a plurality of actuators 81 (various examples of which aredescribed herein). As one example, sensors 16 may include exhaust gassensor 126 located upstream of the emission control device, temperaturesensor 128, and pressure sensor 129. Other sensors such as pressure,temperature, and composition sensors may be coupled to various locationsin the vehicle system 6, as discussed in more detail herein. As anotherexample, the actuators may include fuel injector 66, valve 28, valve 24,and throttle 62. The control system 14 may include a controller 12. Thecontroller may receive input data from the various sensors, process theinput data, and trigger the actuators in response to the processed inputdata based on instruction or code programmed therein corresponding toone or more routines. Example control routines are described herein withregard to FIGS. 8-12.

Hydrocarbon retaining system 22 can operate to store hydrocarbons from aplurality of sources, including the engine exhaust 25 and the fuelsystem 18, concurrently or during different operating conditions. Undersome operating conditions, such as during engine starts when theemission control device is not yet to its light-off temperature (e.g., atemperature at which the device reaches a selected, sufficiently high,conversion efficiency for a particular exhaust constituent), exhaust gasmay be routed from the exhaust 25 to the hydrocarbon retaining system22, and then to the atmosphere through vent 27. In this way, an increaseamount of cold start hydrocarbon emissions may stored in hydrocarbonretaining system 22 while the exhaust gases heat emission control device70. Then, once device 70 reaches sufficient operating temperature,exhaust gases are then routed to atmosphere through conduit 35 and thehydrocarbon retaining system 22 is substantially isolated from theengine exhaust gas. Additionally, fuel vapors generated in the fuel tank20 may be routed to hydrocarbon retaining system 22 for storage beforebeing delivered to the engine intake 25 and combusted in the engine 10.These different storing modes (from the exhaust 25, and from fuel system18) may be carried out concurrently, separately, or combinationsthereof.

After being isolated from the exhaust gas, the hydrocarbon retainingsystem 22 may be coupled to the engine intake to draw fresh air throughvent 27 and purge stored hydrocarbons into the engine intake to becombusted in the engine. Such purging operation may occur duringselected engine operating conditions as described herein.

Additional details of purging and storing operation are describedherein.

FIG. 2 is a schematic diagram showing one cylinder of multi-cylinderengine 10. As described with regard to FIG. 1, engine 10 may becontrolled at least partially by a control system including controller12, as well as by input from a vehicle operator 132 via an input device130. In this example, input device 130 includes an accelerator pedal anda pedal position sensor 134 for generating a proportional pedal positionsignal PP. Combustion chamber, or cylinder, 30 of engine 10 may includecombustion chamber walls 32 with piston 36 positioned therein. Piston 36may be coupled to crankshaft 40 so that reciprocating motion of thepiston is translated into rotational motion of the crankshaft.Crankshaft 40 may be coupled to at least one drive wheel of a vehiclevia an intermediate transmission system. Further, a starter motor may becoupled to crankshaft 40 via a flywheel to enable a starting operationof engine 10.

Combustion chamber 30 may receive intake air from intake manifold 44 viaintake passage 42 and may exhaust combustion gases via exhaust manifold48. Intake manifold 44 and exhaust manifold 48 can selectivelycommunicate with combustion chamber 30 via respective intake valve 52and exhaust valve 54. In some embodiments, combustion chamber 30 mayinclude two or more intake valves and/or two or more exhaust valves. Theintake manifold may include a purge path fluidly coupled to the exhauststream allowing purge vapors to be delivered to the engine intakemanifold 44. While this example shows the purge path downstream of thethrottle to enable manifold vacuum to draw in the gases, various otherconfigurations may also be used. For example, in the case of aturbocharged engine, the purge line(s) may lead to upstream of theturbocharger compressor inlet.

In this example, intake valve 52 and exhaust valves 54 may be controlledby cam actuation via respective cam actuation systems 51 and 53. Camactuation systems 51 and 53 may each include one or more cams and mayutilize one or more of cam profile switching (CPS), variable cam timing(VCT), variable valve timing (VVT) and/or variable valve lift (VVL)systems that may be operated by controller 12 to vary valve operation.The position of intake valve 52 and exhaust valve 54 may be determinedby position sensors 55 and 57, respectively. In alternative embodiments,intake valve 52 and/or exhaust valve 54 may be controlled by electricvalve actuation. For example, cylinder 30 may alternatively include anintake valve controlled via electric valve actuation and an exhaustvalve controlled via cam actuation including CPS and/or VCT systems.

Fuel injector 66 is shown coupled directly to combustion chamber 30 forinjecting fuel directly therein in proportion to the pulse width ofsignal FPW received from controller 12 via electronic driver 68. In thismanner, fuel injector 66 provides what is known as direct injection offuel into combustion chamber 30. The fuel injector may be mounted in theside of the combustion chamber or in the top of the combustion chamber,for example. Fuel may be delivered to fuel injector 66 by a fuel system(not shown) including a fuel tank, a fuel pump, and a fuel rail. In someembodiments, combustion chamber 30 may alternatively or additionallyinclude a fuel injector arranged in intake passage 44 in a configurationthat provides what is known as port injection of fuel into the intakeport upstream of combustion chamber 30.

Intake passage 42 may include throttle 62 having a throttle plate 64. Inthis particular example, the position of throttle plate 64 may be variedby controller 12 via a signal provided to an electric motor or actuatorincluded with throttle 62, a configuration that is commonly referred toas electronic throttle control (ETC). In this manner, throttle 62 may beoperated to vary the intake air provided to combustion chamber 30 amongother engine cylinders. The position of throttle plate 64 may beprovided to controller 12 by throttle position signal TP. Intake passage42 may include a mass air flow sensor 120 and a manifold air pressuresensor 122 for providing respective signals MAF and MAP to controller12.

Ignition system 88 can provide an ignition spark to combustion chamber30 via spark plug 92 in response to spark advance signal SA fromcontroller 12, under select operating modes. Though spark ignitioncomponents are shown, in some embodiments, combustion chamber 30 or oneor more other combustion chambers of engine 10 may be operated in acompression ignition mode, with or without an ignition spark.

Exhaust gas sensor 126 is shown coupled to exhaust passage 48 upstreamof emission control device 70. Sensor 126 may be any suitable sensor forproviding an indication of exhaust gas air/fuel ratio such as a linearoxygen sensor or UEGO (universal or wide-range exhaust gas oxygen), atwo-state oxygen sensor or EGO, a HEGO (heated EGO), a NOx, HC, or COsensor. Emission control device 70 is shown arranged along exhaustpassage 48 downstream of exhaust gas sensor 126. Device 70 may be athree-way catalyst (TWC), NOx trap, various other emission controldevices, or combinations thereof. In some embodiments, during operationof engine 10, emission control device 70 may be periodically reset byoperating at least one cylinder of the engine within a particularair/fuel ratio.

Controller 12 is shown in FIG. 1 as a microcomputer, includingmicroprocessor unit 102, input/output ports 104, an electronic storagemedium for executable programs and calibration values shown as read onlymemory chip 106 in this particular example, random access memory 108,keep alive memory 110, and a data bus. Storage medium read-only memory106 can be programmed with computer readable data representinginstructions executable by processor 102 for performing the methodsdescribed below as well as other variants that are anticipated but notspecifically listed. Controller 12 may receive various signals fromsensors coupled to engine 10, in addition to those signals previouslydiscussed, including measurement of inducted mass air flow (MAF); enginecoolant temperature (ECT) from temperature sensor 112 coupled to coolingsleeve 114; a profile ignition pickup signal (PIP) from Hall effectsensor 118 (or other type) coupled to crankshaft 40; throttle position(TP) from a throttle position sensor; and absolute manifold pressuresignal (MAP) from sensor 122. Engine speed signal, RPM, may be generatedby controller 12 from signal PIP. Manifold pressure signal MAP from amanifold pressure sensor may be used to provide an indication of vacuum,or pressure, in the intake manifold.

As described above, FIG. 2 shows only one cylinder of a multi-cylinderengine 10, and that each cylinder may similarly include its own set ofintake/exhaust valves, fuel injector, spark plug, etc.

FIG. 3 shows a first embodiment 300 of the hydrocarbon retaining systemincluding hydrocarbon retaining devices, such as HC trap 310 arranged inparallel with exhaust conduit 35, downstream of the emission controldevice 70, and canister 322. An exhaust conduit valve 24 is located inthe exhaust conduit for blocking exhaust flow during a first mode, andallowing exhaust flow to pass during a second mode. A bypass conduit 312is coupled upstream and downstream of the exhaust conduit valve 24.Further, the bypass conduit 312 includes a first bypass valve 314, an HCtrap 310, and a second bypass valve 318. In this example the HC trap mayinclude a brick 320. In other examples the HC trap may include aplurality of bricks or other structures, such as activated charcoal.Further, HC trap 310 may also be a canister using micropore (0.5 nm poresize range) activated carbon or zeolites. The bypass conduit 312 leadsto the atmosphere through vent 27, and optionally through valve 318 andconduit 35.

Furthermore, the HC trap 310 may be fluidly coupled to a purge canister322 via passage 324. The purge canister 322 may be configured to collectvapor from the fuel system, such as via a conduit 328 leading to thefuel tank 20. The passage 324 may include a valve 326. The purgecanister 322 may also be fluidly coupled to the engine intake via aconduit 330 and valve 332. Similar to the HC trap 310, the canister 322may include activated charcoal, although it may have a different, e.g.,high, porosity.

While this example shows two hydrocarbon retaining devices (e.g., HCtrap 310 and purge canister 322), various alternatives may be provided.For example, a single hydrocarbon retaining device, such as a canister,may be used, where the canister operates to store both exhausthydrocarbons as well as fuel tank vapors. Further, the two hydrocarbonretaining devices may each be canisters, or may each be HC traps.Irrespective of the particular configuration of the HC retaining system,the hydrocarbon retaining devices can receive routed cold starthydrocarbons and retain the hydrocarbons.

In one example, the hydrocarbon retaining devices may comprise granularactivated carbon contained in a plastic housing, since the exhaust gastemperatures may be substantially lower than the full range of exhausttemperature experienced in the exhaust system.

The hydrocarbon retaining system 22 of FIG. 3 may be operated by acontroller in a plurality of modes by selective adjustment of thevarious valves. For example, the following operating modes may beperformed:

MODE A: Exhaust Hydrocarbon Storage

During select engine and/or vehicle operating conditions, the controller12 may close valves 24 and 326, and open valves 314 and optionally 318.Additionally, valve 332 is closed. Example operating conditions includecold engine starting operation before the emission control device hasreached a light-off temperature. In this mode, exhaust from engine 10 isrouted through HC trap 310 before exiting to the atmosphere via vent 27,while the purge canister 322 is isolated from the exhaust gas andhydrocarbon retaining system.

MODE B: Fuel Vapor Storage

During select engine and/or vehicle operating conditions, the controller12 may open valve 24 and 326, and close valves 314 and 318. Valve 332may be closed, in which case fuel tank vapors are merely stored, and notpurged. Alternatively, valve 332 may be open to a controlled amount,such that some fuel tank vapors are stored and some are delivered to theengine for combustion. In this mode, at least some fuel tank vapors arerouted through and retained in both purge canister 322 and HC trap 310before being vented through vent 27. As such, the fuel tank may becommunicated to the hydrocarbon retaining system.

MODE C: HC Trap and/or Canister Purging

During select engine and/or vehicle operating conditions, the controller12 may open valve 24 and 326, and close valves 314 and 318.Additionally, valve 332 may be open to a controlled amount, such thatfresh air is drawn through vent 27 to purge HC trap 310 and purgecanister 322 through 330 and valve 332 to the engine intake 25. In thismode, the purged fuel vapors from the canister and/or HC trap arecombusted in the engine, while exhaust gas is routed through conduit 35to the atmosphere after treatment by the emission control device.

In an alternative embodiment, rather than drawing in fresh air via vent27 to purging stored hydrocarbons, the system may additionally oralternatively route exhaust gases to the vent to enable heated exhaustto heat the hydrocarbon retaining system and better purge storedhydrocarbons. Such operation may be used during specific conditions,such as cold ambient temperatures. Further, under some conditions, thesystem may intentionally route exhaust gases during the storing mode fora longer duration to heat the hydrocarbon retaining system to a highertemperature, thereby improving the subsequent purging operation. In oneexample, before a purging operation, exhaust gases may be routed to thehydrocarbon retaining system (even during non-starting conditions) toincrease temperature and improve the subsequent purging efficiency. Thisoperation may be used when temperature of the hydrocarbon retainingsystem falls below a threshold value, or when reduce purgingopportunities are present.

Note the configuration of FIG. 3 enables the gas flowing through the HCtrap 310 to be routed back to the exhaust 35 and out the tailpipe. Thus,by using the valve 318 (which can be a lower temperature, lower costvalve compared to other exhaust valves in the system) that allows theexhaust flow to return to the exhaust pipe (or be routed to a tailpipelocation), various advantages may be achieved. For example, theconfiguration allows for sufficient flow during the cold start trappingoperation without sending exhaust gas to another location other than thetailpipe. Further, by providing a separate port for the purge flowinlet, it is possible to draw purge air from a location that is lesssusceptible to water ingestion.

Additionally, when the exhaust gas is routed back to the exhaust systemas shown in FIG. 3, the HC trap can be positioned upstream of themuffler, thus reducing effects of muffler leakage on the emission systemperformance.

FIG. 4 shows a second embodiment 400 of the hydrocarbon retaining system22. In this configuration, a valve 24 includes a diverter valve thateither routes exhaust gas through conduit 35 to the atmosphere, or toconduit 412. FIG. 4 shows HC trap 410 arranged in parallel with exhaustconduit 35, downstream of the emission control device 70. Conduit 412 iscoupled upstream of the valve 24 and includes HC trap 410.

Furthermore, the HC trap 410 may be fluidly coupled to a purge canister422 via passage 424 and valve 426. The purge canister 422 may beconfigured to collect vapor from the fuel system, such as via a conduit428 leading to the fuel tank 20). The purge canister 422 may also befluidly coupled to the engine intake via a conduit 430 and valve 432.The hydrocarbon retaining system 22 may also include a first pressuresensor 436 and a second pressure sensor 438 coupled to conduit 424.Additionally, an HC trap temperature sensor 440 may be coupled directlyto the HC trap.

As shown schematically in FIG. 4, vent 27 is thermally coupled to atleast a portion of conduit 35 so that heat is transferred therebetween.In one example, the vent 27 may be spatially adjacent to at least aportion of conduit 35.

The hydrocarbon retaining system of FIG. 4 may be operated by acontroller in a plurality of modes by selective adjustment of thevarious valves. For example, the following operating modes may beperformed:

MODE A: Exhaust Hydrocarbon Storage

During select engine and/or vehicle operating conditions, the controller12 may adjust valve 24 to divert exhaust gas to conduit 412, as well asclose valves 432 and 426. Example operating conditions include coldengine starting operation before the emission control device has reacheda light-off temperature. In this mode, exhaust from engine 10 is routedthrough HC trap 410 before exiting to the atmosphere via vent 27, whilethe purge canister 422 is isolated from the exhaust gas and hydrocarbonretaining system.

MODE B: Fuel Vapor Storage

During select engine and/or vehicle operating conditions, the controller12 may adjust valve 24 to direct exhaust gas through conduit 35, andisolate the hydrocarbon trap 410 from exhaust gas. Additionally, thecontrol may open valve 326, and close valve 432. In this mode, at leastsome fuel tank vapors are routed through and retained in both purgecanister 422 and HC trap 410 before being vented through vent 27.

MODE C: HC Trap and/or Canister Purging

During select engine and/or vehicle operating conditions, the controller12 may adjust valve 24 to direct exhaust gas through conduit 35, andisolate the hydrocarbon trap 410 from exhaust gas. Additionally, thecontrol may open valve 326, and controllably open valve 432 such thatfresh air is drawn through vent 27 to purge HC trap 410 and purgecanister 422 through 430 and valve 432 to the engine intake 25. In thismode, the purged fuel vapors from the canister and/or HC trap arecombusted in the engine, while exhaust gas is routed through conduit 35to the atmosphere after treatment by the emission control device. Asnoted above, heat may be transferred to the fresh air inducted to vent27. In some examples heat may be transferred through conduction,convection, forced convection, combinations thereof, or alternativeforms of thermal communication. In this way, when the system is warmingup to operating temperature, the warmed air may improve release ofhydrocarbons stored in HC trap 410 and/or purge canister 422.

FIG. 5 shows a schematic depiction of a third embodiment of thehydrocarbon retaining system 22. This embodiment is similar to that ofFIG. 3, except that the HC trap 510 includes two bricks 520, and isconfigured to pass exhaust gasses serially through the bricks, but purgethem in parallel. Specifically, the system of FIG. 5 includes HC trap510 arranged in parallel with exhaust conduit 35, downstream of theemission control device 70. An exhaust conduit valve 24, which in thisexample may be a throttle, is located in the exhaust conduit forblocking exhaust flow during a first mode, and allowing exhaust flow topass during a second mode. A bypass conduit 512 is coupled upstream anddownstream of the exhaust conduit valve 24. Further, the bypass conduit512 includes a first bypass valve 514, the HC trap 510, and a secondbypass valve 518. The bypass conduit 512 is also coupled to vent 27 viatwo parallel passages 534 and valve 538.

Furthermore, the HC trap 510 is fluidly coupled to a purge canister 522via passage 524. The purge canister 522 may be configured to collectvapor from the fuel system, such as via a conduit 528 leading to thefuel tank 20 (not shown). The purge canister 522 may also be fluidlycoupled to the engine intake via a conduit 530 and valve 532.

The hydrocarbon retaining system of FIG. 5 may be operated by acontroller in a plurality of modes by selective adjustment of thevarious valves. For example, the following operating modes may beperformed:

MODE A: Exhaust Hydrocarbon Storage

During select engine and/or vehicle operating conditions, the controller12 may close valves 24 and 538, and open valves 514 and 518.Additionally, valve 532 is closed. Example operating conditions includecold engine starting operation before the emission control device hasreached a light-off temperature. In this mode, exhaust from engine 10 isrouted through HC trap 510 (sequentially through bricks 520 a and then520 b) before exiting to the atmosphere via conduit 35, while the purgecanister 522 is effectively isolated from the exhaust gas as the flow isdeadheaded against valve 526.

MODE B: Fuel Vapor Storage

During select engine and/or vehicle operating conditions, the controller12 may open valve 24, 526, and 538, and close valves 514 and 518. Valve532 may also be closed. The exhaust gases are thus isolated from thecanister 522 and HC trap 510. In this mode, at least some fuel tankvapors are routed through and retained in both purge canister 522 and HCtrap 510 before being vented through valve 538 and vent 27. Inparticular, the fuel vapors are first routed through canister 522 andthen routed, in parallel through bricks 520 a and 520 b, respectively,before being vented through 27. In this way, fuel tank vapors may bestored in different concentrations at different locations of the traps,due to the different direction of flow of exhaust gas and fuel tankvapors, at least from brick 510 a.

MODE C: HC Trap and/or Canister Purging

During select engine and/or vehicle operating conditions, the controller12 may open valve 24 and 538, and close valves 514 and 518.Additionally, valve 532 may be open to a controlled amount, such thatfresh air is drawn through vent 27 to purge HC trap 510 and purgecanister 522 through 530 and valve 532 to the engine intake 25. In thismode, the purged fuel vapors from the canister and/or HC trap arecombusted in the engine, while exhaust gas is routed through conduit 35to the atmosphere after treatment by the emission control device. Again,in flow movement opposite to that of MODE B of FIG. 5, fresh air isrouted in parallel to bricks 520 a and 520 b, before being combined androuted through purge canister 522. In this way, purging of vapors occursin a direction opposite to that of fuel tank vapor storing in bothbricks, and opposite to the direction of exhaust gas hydrocarbon storingin at least one brick (520 a).

Such differential storing and purging directions, making use of bothserial storing and parallel purging, can enable improved storage andrelease, thus increasing efficiency of the engine and emission system.

FIG. 6 shows additional details of an example of the third embodiment ofFIG. 5. Similar components are labeled accordingly. In this example,valves 24, 518, and 514 are vacuum actuated throttle valves. The HC trapincludes two bricks 520 a,b having activated carbon pellets 612. Avacuum regulator 614 is coupled to the valves 24, 514, and 518, and maybe configured to closed valve 24 whenever valves 518 and 514 are open,and vice versa. The vacuum regulator 614 may be electronically actuatedby controller 12 in one example.

Continuing with FIG. 6, a first pressure sensor 540 and a secondpressure sensor 542 are coupled to the intake 616 and outlet 618 of theHC trap. On Board Diagnostic (OBD) sensor 620 may be coupled between thefirst and the second bricks, 520 a and 520 b, respectively. The OBDsensor may measure the gas pressure, composition, or a combinationthereof in the HC trap.

In this example, HC trap 510 may be located after an underbody catalystcan but before a muffler. Further, the length of the conduits fromexhaust 35 can be >12 inches to reduce the exhaust gas temperature from800° C. to 100° C. and to permit plastic components. Further, carbon mayfurther operate to reduce noise when bypassing a muffler in the exhaust.

Continuing with one example, the exhaust flaps at the canister inlet andoutlet (616, 618) can be plastic and can be integrated into a plastichousing of the trap/canister. The device may include a rubbergasket/o-ring to help seal around the housing where the flap would closeor around the plastic flap due to reduced temperature. The housing ofdevice 510 may comprise 1.5″ ID entry/exit tubes, molded bosses in thespring section for a sensor and poppet valve, molded ports on the conesfor air intake, screens on both sides of the carbon bed to allow flowthrough the canister and actuated exhaust flaps. The inlet valve coupledto 524 may be located between the packed beds. At that spot, OBD sensor620 can observe loading and unloading of the beds. If the plasticexhaust flaps seal, the poppet valve will let in air from the aircleaner box, in one example. The fresh air inlet at each cone is splitfrom the inlet air source downstream of the vent valve. The outlet maylead to the fuel tank vapor purge system, either in series into thecanister 522, for example, or in parallel thereto.

FIG. 7 shows a fourth embodiment of a hydrocarbon retaining system 22.This example is similar to that of FIG. 4, although different valve andconduit configurations are used, along with two HC traps, in bypass 712.Specifically, in this example, valve 24 operates as a diverter valve toeither allow exhaust gas flow through conduit 35 to atmosphere, or todirect the exhaust gas flow to conduit 714 and valve 716. In thisexample, valve 716 is another diverter valve which either allowscommunication between conduit 714 and conduit 740, or conduit 714 andconduit 742. Bypass 712 further includes a first and second HC trap, 726and 728, respectively. Further still, a valve 726 is shown forcontrolling flow leading to, or coming from, the purge canister (notshown), which then leads to the fuel tank and intake manifold, similarto the other example configurations described above. As such, fuelvapors from the fuel tank may be routed to the first and second traps,726 and 728, in that order, and purged in the opposite order.

In FIG. 7, the two traps 726 and 728 are configured with different HCtrapping characteristics. For example, trap 726 may be of a largerporosity activated carbon to capture larger HC molecules as compared totrap 728. In this way, during storage, the gases may be routed firstthrough 726 and then through 728, such that HC molecule size in the gasis progressively reduced. Additionally, since stored HC molecules may bedifficult to remove from the smaller pore activated carbon, the smallerpore activated carbon may be buffered by the larger pore size activatedcarbon to inhibit HC molecules from irreversibly absorbing into thesmaller pores. Furthermore, the adsorption of smaller HC species intotrap 728 may occur at higher pressures. As such, the inlet pipingdiameter from the diverter valve 716 to the traps may be sizedsufficiently to provide a desired pressure during storage and purgeoperation.

The configuration of FIG. 7 also provides for opposite flow directionfor storage and purging operation, for both traps 726 and 728.Specifically, during storage of HC in the exhaust gas, the divertervalves 24 and 716 route the exhaust gas through 714 and then to trap726, and then 728, before being vented via 27. During purging of thetraps, the valves are adjusted to route fresh air through vent 27, trap728, and then trap 726, before being delivered through 726 and then tothe intake. In this way, improved storage and release of HC can beachieved, especially in light of the differential characteristics (e.g.,porosity) of the traps. The configuration of FIG. 7 can thus operate inany of MODES A, B, and C.

While 726 and 728 may each be HC traps in one example, two charcoalcanisters may also be used. Alternatively, as noted, zeolites can beincluded. For example, canister 726 may be configured to adsorbcold-start propylene and higher mass hydrocarbons rather than a separatedevice. Micro-pore activated carbons in 728 adsorb lower sizedhydrocarbons, but can be more protected than 726 in series.Additionally, purging of the traps with preheated air from an aircleaner box or hot vehicle exhaust, in counter-current flow relative tothe adsorption flow direction, can further provide improved performance.

While this example shows two traps in the configuration of FIG. 7, moreor less may be used.

In one particular example, device 726 can include a carbon canister (oflarger porosity) to capture medium to large sized HC molecules, followedby a smaller pore activated carbon canister 728. During storage, gasesfirst pass through 726, and then to 728. Removal is performed in theopposite direction. In this way, the larger pores better protect thesmaller pores and reduce irreversible adsorption of larger HC moleculesinto the smaller pores. The adsorption of small HC species into thesmall pore medium may better respond to pressure, such as approximately5 MP, which can be provided by sizing of the inlet piping diameter fromthe diverter valve to the canisters. Similarly, removal of the HCspecies may benefit from increased temperature, such as through heattransfer from exhaust gas, or by using at least some exhaust gas, suchas during idle conditions.

It should be appreciated that with regard to FIGS. 3-7, MODE A may notonly operate to store HC from the exhaust in the hydrocarbon retainingsystem, but it may also substantially heat the system. This may beadvantageously used to thus prepare the hydrocarbon retaining system 22for subsequent purging operation, as increased temperature can act tomore easily release stored hydrocarbons.

Further, while the examples of FIGS. 3-7 show combined purging of thefuel tank vapors and stored exhaust hydrocarbons, in alternativeconfigurations these may be purged independently. For example, theexample HC traps may be purged via a purge line in parallel with a purgeline of the example canisters, to thereby enable separate and/orindependent purging of the different hydrocarbon storage systems. Forexample, one hydrocarbon retaining device may be purged without purginga second hydrocarbon retaining device. Further still, in some exampleconfigurations of FIGS. 3-7, the fuel tank vapors in the purge canisterscan be purged sufficiently faster than the hydrocarbons in the HC traps.As such, during initial purging, the learned vapor amount/concentrationcan be used to determine the amount of fuel vapors stored in thecanister, and then, during a later portion of the purging operation(when the canister is sufficiently purged/empty), the learned vaporamount/concentration can be used to estimate a loading state of the HCtraps (that was generated during the most recent storing operation, suchas the most recent cold start event).

Further still, while the examples of FIGS. 3-7 show non-concurrentstoring of exhaust gas hydrocarbons and purging of the retaining system22, in alternative embodiments, some stored hydrocarbons may be purgedduring storage of other hydrocarbons.

The following method of FIGS. 8-14 may be implemented using systems,components, and devices described herein, but alternatively may beimplemented using other suitable systems, components, and devices.

Referring now to FIG. 8, a routine 800 is shown for controlling engineoperation, fuel vapor management, and exhaust emission management.Routine 800 may operate during a warm-up condition, such as while theengine or exhaust warms from ambient temperatures to it normal operatingtemperature range.

First, at 810, the routine determines whether an engine start ispresent. For example, the routine may determine whether the engine isbeing started from rest. Additionally, or alternatively, the routine maydetermine whether the engine has been started via engine crankingoperation. When an engine start is present, the routine continues to812, where the routine estimates or measures emission control devicetemperature based on various parameters. In one example, the routine maydetermine emission control device temperature based on an engine offtime (soak time), ambient temperature, engine coolant temperature, andintake air charge temperature. Alternatively, or in addition, theroutine may determine emission control device temperature based on oneor more exhaust gas temperature sensors located in exhaust passage 35 orexhaust manifold 48. Further still, the routine may determinetemperature of an emission control device based on a temperature sensormounted to the emission control device.

In 814, the routine determines a temperature threshold value based onoperating conditions. One example approach for determining thetemperature threshold is described herein with regard to FIG. 9.Alternatively, a fixed temperature threshold may be used. In oneexample, the temperature threshold correlates to a catalyst light-offtemperature. Next, the routine continues to 816 to determine whetherstorage of exhaust generated hydrocarbons in the retaining system 22 isenabled, and if not, to end such routing. Such operation may be adjustedbased on various conditions, including whether a capacity of hydrocarbonstorage of the retaining system 22 is greater than a threshold value.For example, the routine may enable storage in the retaining system 22when the storage system 22 has been purged during previous engineoperation. Additionally, the routine may enable storage of hydrocarbonsin retaining system 22 when temperature of retaining system 22 is lessthan a maximum storage temperature. Further, the routine may enablestorage of exhaust hydrocarbons in retaining system 22 as based on afuel property of the fuel combusted in the engine, such as an alcoholamount in the fuel, where the alcohol amount in the fuel may be learnedduring previous engine operation. In this way, the ending of the routingof exhaust gas to the hydrocarbon retaining system 22 may be adjusted totake advantage of the different storage characteristics of differentfuels. For example routing may continue up to higher storage amounts, orfor a longer duration, when combusting higher alcohol content fuels ascompared to lower alcohol content fuels. Further still, the routine mayenable storage of hydrocarbons in retaining system 22 when an enginesoak time (e.g., an engine/vehicle off-duration) is greater than athreshold amount. In this way, during hot re-starts, for example, theengine start may direct exhaust gases through exhaust system 35 andbypass the retaining system 22.

When the answer to 816 is yes, the routine continues to 818 to determinewhether temperature of emission control device 70 is less than thethreshold temperature determined in 814. If so, the routine continues to820 to operate one or more of the exhaust valves (e.g., 24) to directexhaust gas through the hydrocarbon retaining system 22, and inparticular through one or more hydrocarbon traps. For example, dependingon the system configuration, control system 14 may adjust one or moreexhaust valves to route exhaust gas from downstream of emission controldevice 70 to and through the hydrocarbon retaining system 22 beforebeing vented or routed to the atmosphere. In one example, the routineoperates the system in MODE A, described above herein. Further, thesystem may operate with spark timing substantially at a peak torquetiming, or may operate with an amount of spark retard, depending onoperating conditions as described herein with regard to FIG. 10, forexample.

Next, in 822, the routine estimates an amount of hydrocarbon stored inthe hydrocarbon retaining system 22, such as the amount of hydrocarbonstored in HC trap 310. The routine may estimate the amount of storedhydrocarbons based on exhaust gas flow rate, exhaust temperature,temperature of hydrocarbon retaining system 22, engine speed, andvarious other parameters.

When the answer to either 816 is no or 818 is yes, the routine continuesto 824 to operate the exhaust valves to direct exhaust gas from theemission control device 70 to bypass the hydrocarbon retaining system 22and be delivered to the atmosphere through conduit 35. Also, as notedherein, the exhaust gas may be routed through various additionalemission control devices and/or mufflers before being delivered to theatmosphere. In one example during the operation of 824, the routineoperates the engine to increase exhaust gas temperature thus retardingignition timing sufficiently past MBT timing as well as performingcombustion at a slightly lean air-fuel ratio in the combustion chamber.Further, the operation of 824 may thus result in the system notoperating in MODE A, although the system may or may not operate in MODESB and C, as described further herein with regard to FIG. 8.

From 824 or 822, the routine continues to 826 to determine whetherpurging of stored hydrocarbons from the hydrocarbon retaining system 22should be carried out (for example, whether the system can operate inMODE C). In one example, the routine of FIG. 11 shows one example ofdetermining whether to purge the hydrocarbon retaining system 22.Initiating the purging of the hydrocarbon retaining system 22 may bebased on various engine and vehicle operating parameters, including theamount of hydrocarbon stored in the retaining system 22 (such as theamount of hydrocarbons stored in HC trap 310), the temperature of theemission control device 70, temperature of the hydrocarbon retainingsystem, fuel temperature, the number of starts since the last purge,fuel properties (such as the alcohol amount in the combusted fuel), andvarious others. In one example at 826, the routine determines whetherexhaust gases were routed to the hydrocarbon retaining system 22 duringthe current engine start. In one particular example, the initiating ofthe purging may be adjusted to be initiated at higher temperatures asthe alcohol amount in the fuel increases.

When the answer to 826 is yes, the routine continues to 828 to operatethe exhaust valves to draw fresh air through hydrocarbon retainingsystem 22 and into intake passage 42 of engine 10, which may includeoperating the system in MODE C. Engine 10 then operates to induct thevapors along with injected fuel and intake air, and perform combustionthereof. Next, in 830, the routine estimates the amount of purgedhydrocarbons from the hydrocarbon retaining system 22 (which may beattributed to one or both of an HC trap and purge canister) based onvarious parameters including the amount of stored hydrocarbons, as wellas feedback information from exhaust air-fuel ratio sensors. In oneexample, feedback from an exhaust gas oxygen sensor may be used to learnor update the estimated amount of hydrocarbons stored in the HC trap todetermine degradation of the HC trap based on such an estimate. Further,the routine may also adjust throttling of the engine to adjust an amountof purge gases drawn through a purge canister, HC trap, or both.

When the answer to 826 is no, or from 830, the routine continues to 832.At 832, the routine determines whether to purge hydrocarbon vaporsgenerated from the fuel tank, in the event that such vapors were notpurged at 828, or were not sufficiently purged at 828. One exampleroutine for determining whether to purge fuel tank generated vapors isdescribed herein with regard to FIG. 12. When the answer to 832 is yes,the routine continues to 834 to operate the exhaust valves to purge fueltank generated vapors from the hydrocarbon retaining system 22, whichmay include operating the system in MODE C. Otherwise when the answer to832 is no, or from 834, the routine continues to the end.

While not illustrated specifically in FIG. 8, the control system mayalso operate the system in MODE B whenever the system is not operatingin MODE A or C. Alternatively, MODE B may be selectively enabled basedon various operating conditions, including ambient temperature, fueltemperature, and others.

Additionally, by appropriate temperature considerations, it is possibleto further provide control of routing of exhaust gas to the hydrocarbonretaining system, and purging of the hydrocarbon retaining system to theengine intake, to account for warm engine restart conditions. Forexample, the system may consider engine coolant temperature and catalysttemperature in the enabling of the routine and initiation of the purgingsuch that if coolant temperature is above a warm re-start thresholdand/or catalyst temperature is above a warm re-start threshold, therouting of exhaust gas to the hydrocarbon retaining system is disabledand purging is initiated once engine crank/run-up is completed.

Referring now to FIG. 9, routine 900 is described for determining atemperature threshold below which exhaust gases may be routed tohydrocarbon retaining system 22. First, at 910, the routine determines afuel composition. In one example, the routine may determine an alcoholconcentration and/or fuel blend of the fuel stored in tank 20. Thealcohol concentration may be learned based on feedback from exhaust gasoxygen sensors indicating a shift in the stoichiometric air-fuel ratio.Additionally, or alternatively, the routine may determine an alcoholconcentration of the fuel based on a fuel concentration sensor. Notethat the routine may determine a relative alcohol amount in a gasolinefuel, or various other fuel compositions.

Next, at 912, the routine determines a fuel temperature. In one example,the routine may measure fuel temperature from a fuel temperature sensorcoupled to fuel tank 20. Alternatively, the routine may estimate fueltemperature based on various parameters, including engine coolanttemperature, ambient air temperature, and/or various others.

Next, at 914, the routine determines a temperature threshold based onthe fuel temperature and composition/makeup of 912 and 910,respectively. Additionally, the routine may determine the thresholdbased on additional operating conditions, including aging of catalyticmaterial of the emission control device 70. In one example, the routinemay increase the temperature threshold as the amount of alcohol in thefuel blend increases. In this way, it is possible to adjust thetemperature range at which exhaust gas is routed to a hydrocarbon trapin the hydrocarbon retaining system 22. Specifically, such operation cantake advantage of the different storage properties of the trap as theamount of alcohol in the fuel varies. For example, fuels may havedifferent adsorption and/or desorption characteristics with varyingalcohol content. Also, water in the exhaust may affect temperature atwhich storage/release of hydrocarbon species occurs. As the alcoholcontent of the fuel varies, different HC chains may be produced in theexhaust, thus generating the different storage/release characteristics.In one particular example, HCs may be trapped up to higher temperatureswith increase alcohol content in the fuel, and therefore the terminationor reduction of operation in MODE A may be delayed to higher temperaturewith increase alcohol content in the fuel.

Referring now to FIG. 10, it shows an example routine 1000 forcontrolling combustion air-fuel ratio during engine starting based onthe mode of exhaust gas routing, and/or hydrocarbon retaining systempurging.

First, at 1010, the routine determines whether the engine is starting,such as described with regard to 810. If so, the routine continues to1012 to determine whether the system is directing gas to hydrocarbonretaining system 22 (e.g., whether MODE A operation is present). If so,the routing continues to 1014 to select combustion air-fuel ratio basedon engine coolant temperature, as well as various other parameters.Next, at 1016, the routine operates at the selected air to fuel ratiowith decreased or no spark retard, such as by operating at MBT timing,potentially even during conditions where temperature of the emissioncontrol device (e.g., catalytic converter in the exhaust) issubstantially below its light-off temperature. In one example, theair-fuel ratio selected at 1014 may initially, during the start, beslightly lean, and after cranking and run up of engine speed, theselected air-fuel ratio may be approximately stoichiometry, or slightlyrich. Alternatively, the air-fuel ratio may be selected based on theamount of hydrocarbons stored in hydrocarbon retaining system 22 (suchas the amount of hydrocarbons stored in HC trap 310). For example, asthe amount of hydrocarbon stored in the hydrocarbon retaining system 22increases, the combustion air-fuel ratio may be correspondingly adjustedhigher, (e.g., less rich, or more lean).

When the answer to 1012 is no, the routine continues to 1018 todetermine whether temperature of the emission control device 70 is lessthan a light off temperature. When the answer to 1018 is no, the routinecontinues to operate the engine to combust approximately stoichiometricair-fuel ratio with selective adjustment of spark retard (e.g.,substantially no spark retard, unless needed for knock abatement, torquereduction, etc.). Alternatively, when the answer to 1018 is yes, theroutine continues to 1022 to operate the engine to combust a nearstoichiometric or slightly lean air-fuel ratio with ignition timingretarded more than operation at 1016 and/or 1020. Otherwise, at 1020,the routine operates the engine to combust a stoichiometric air-fuelratio with selective adjustment of spark retard, with less retard thanat 1022. For example, the ignition timing may be retarded an amountbased on catalyst temperature.

As still another example, the system may thus operate in a plurality ofignition timing retard modes based on whether exhaust gasses are routedto the hydrocarbon retaining device. For example, the modes may includea first mode where the routine routes exhaust gases to the hydrocarbonretaining system and operates during at least a portion of first modewith spark at a first timing, and with a first engine/exhaust air-fuelratio; and a second mode where the routine bypasses the hydrocarbonretaining system and operates during at least a portion of the secondmode with spark at a second timing more retarded than first timing or asecond engine/exhaust air-fuel ratio leaner than the first exhaustair-fuel ratio. In one particular example, the second mode is performedafter the first mode, both during a common engine start, and where thefirst mode is performed at a lower temperature of the emission controldevice than the second mode. Further, the first air-fuel ratio may belean during a first portion, and stoichiometric or rich during a secondportion of the first mode. Alternatively, the first mode may beperformed during a first engine start, and the second mode may beperformed during a second engine start, where during the second start,the hydrocarbon retaining system may have a greater amount ofhydrocarbons stored than during the first start.

Next, at 1024, from 1020, the routine determines whether purging of theretaining system 22 is present, including purging of one or both ofstored fuel tank vapors and stored exhaust gas hydrocarbons. If so, theroutine continues to 1026 where the control system adjusts the fuelinjection amount responsive to feedback from one or more exhaust gasoxygen sensors to maintain stoichiometric combustion and learning anamount of hydrocarbons being purged from and/or an amount ofhydrocarbons stored in, retaining system 22. Additionally, the routinemay adjust the throttle position responsive to an amount of fresh airdrawing through the hydrocarbon retaining system. For example, theroutine may close the throttle when initiating the purging operation tocompensate for additional flow.

In one example, the engine may provide a desired air-fuel ratio byoperating some cylinders leaner than the desired air-fuel ratio (e.g.,stoichiometric), and some cylinders richer than the desired air-fuelratio. Such operation may be advantageous in that it can generateadditional exothermic exhaust heat, while still providing astoichiometric exhaust air-fuel ratio. In one example, such splitair-fuel ratio operation may be provided during 1016, for example, toenable increased heating of the emission control device. Further, byutilizing an HC trap in the retaining system 22, for example, anyremaining hydrocarbons exiting the device 70 can be trapped to maintaindesired emission levels.

Referring now to FIG. 11, a routine is described for determining whetherto purge the exhaust generated hydrocarbons from retaining system 22. Inone example, the routine of FIG. 11 determines whether to end fuel tankvapor storage (e.g., MODE B) and transition to purging (e.g., MODE C).

First, in 1110, the routine determines whether a HC retaining device,such as an HC trap or canister, of system 22, was operated to storehydrocarbons during the engine start. If so, the routine continues to1112 to determine whether the system is purging fuel tank vapors. Ifnot, the routine continues to 1114 to determine whether an exhausttemperature, such as the temperature of the emission control device, isgreater than a threshold temperature, such as the threshold of 818. Forexample, the threshold may be adjusted based on the alcohol content offuel in the fuel tank and injected into the engine.

If the answer to 1114 is yes, the routine continues to 1116 to determinewhether the amount of stored hydrocarbons in the retaining system 22(for example the amount of hydrocarbons stored in HC trap 310) isgreater than a threshold value. If so, the routine continues to 118 todetermine whether the air-fuel ratio of combustion in engine 10 isapproximately the stoichiometric ratio. If so, the routine continue to1120 to purge the retaining system, such as to purge an HC trap and/orcanister (e.g., operate in MODE C).

In one example, the operation of FIG. 11 may be carried out after enginestarting, or during starting conditions, such as during hot re-startconditions.

Referring now to FIG. 12, a routine is described for determining whetherto purge the fuel tank generated hydrocarbons from retaining system 22.In one example, the routine of FIG. 12 determines whether to end fueltank vapor storage (e.g., MODE B) and transition to purging (e.g., MODEC). In one example, the routines of FIGS. 11 and 12 may be coordinatedtogether, such as where fuel tank vapor purging and exhaust gasgenerated hydrocarbon purging occur concurrently. In another example,the routines of FIGS. 11 and 12 are carried out independently, such aswhere fuel tank vapor purging and exhaust gas generated hydrocarbonpurging occur independently.

First, in 1210, the routine determines whether an HC retaining device,such as an HC trap or canister, of system 22, is being purged. If so,the routine ends. Otherwise, the routine continues to 1212 to determinewhether an engine start is present, such as described herein. If not,the routine continues to 1214 to coordinate fuel vapor purging withadaptive learning of fuel injector errors, MAF sensor errors, etc., andthen the routine continues to 1216 to carry out purging of fuel tankvapors to the intake, as coordinated in 1214.

When the answer to 1212 is yes, the routine continues to 1218 todetermine whether the combustion air-fuel ratio is approximately thestoichiometric air-fuel ratio (see FIG. 10). If not, the routine doesnot enable purge, such as when HEGO sensors are used, since it may bedifficult to control air-fuel ratio in the presence of purgingoperation. If so, the routine continues to 1220 to determine whether thesystem is currently operating to direct exhaust gases through theretaining system 22. If so, the routine ends (in the case where purgingand storage occur non-concurrently). Otherwise, the routine continues to1216 to purge the retaining system to the intake.

Referring now to FIG. 13, a routine is described for determining whetherto route exhaust gases to the hydrocarbon retaining system 22 duringconditions other than engine starting operation, such as other engineoperating conditions where the engine conditions to spin and/or thevehicle is traveling. The routine of FIG. 13 may be used after enginestarting/warm-up operations, such as those described above herein.

For example, the operation described with regard to FIG. 13 may beadvantageous during cylinder valve deactivation conditions of one ormore cylinders (e.g., variable displacement engine (VDE) operation)where temperature of an emission control device may drop below anactivation or light-off temperature. Under such conditions, theremaining active cylinders may operate stoichiometric or slightly rich,and the exhaust gas routed to retaining system 22 for storage of excesshydrocarbons exiting the cooled emission control device. Further, it maybe advantageous during deceleration fuel shut-off (DFSO) operation orafter reactivation of DFSO cylinders, where a significant amount offresh, oxygen rich gas is stored in the emission control device, therebyreducing its catalytic reaction of emissions from the engine, as well asits temperature. This can be especially advantageous when reactivatingcombustion after DFSO, where combustion air-fuel ratio duringreactivation is substantially rich to reduce the stored oxygen andre-establish the catalyst's desired oxygen storage state. The operationof FIG. 13 may also be used during catalyst over-temperature conditions(such as when catalyst temperature is above its maximum allowedtemperature for the current conditions) where the engine is operatedrich to reduce the catalyst temperature.

In still another example, the routine of exhaust gases to thehydrocarbon retaining system 22 during conditions other than enginestarting operation may be used to heat the hydrocarbon retaining system22 for subsequent purging. For example, once the hydrocarbon retainingsystem 22 is sufficiently heated, purging operation may be enabled. Thiscan be advantageous when the hydrocarbon retaining system 22 is below athreshold temperature, and would otherwise result in slow and/orinefficient hydrocarbon release and/or desorption.

Referring now specifically to FIG. 13, at 1310 the routine determines at1310 whether an engine start is present, such as described herein. Ifso, the routine continues to 1312 to determine whether the hydrocarbonretaining system 22 has been purged since the engine start of thepresent engine operation and/or whether the amount of hydrocarbons andfuel vapors estimated to be stored in the system 22 is less than athreshold value. For example, the routine may determine whether theamount of hydrocarbons stored in the HC trap 310 is less than athreshold value.

If so, the routine continues to 1314 to determine whether selectconditions are present. In one example, the select conditions includewhen an increased potential for hydrocarbon breakthrough from emissioncontrol device 70 is greater than a threshold. In another example, theselect conditions include deceleration fuel shut-off of one or morecylinders, and/or reactivation from such conditions. In still anotherexample, the select conditions include when the exhaust air-fuel ratiofrom the engine is sufficiently rich of stoichiometry (e.g., richer thana threshold). In yet another example, the select conditions include whenone or more cylinders is deactivated, such as when intake and exhaustvalves are held closed throughout the cycle 4-stroke cycle. If so, theroutine continues to 1316 to operate the exhaust valves to route exhaustgas through the hydrocarbon retaining system 22 (e.g., operate in MODEA).

In this way, improved emission may be achieved, even during non-enginestarting conditions. Further, it will be appreciated that additionalpurging, after the storing operation of 1316, may be carried out duringsubsequent engine operation once the operation at 1316 is ended.

In one particular example, during conditions other than an engine start,where the catalytic emission control device is above its light-offtemperature, the routine may route exhaust gas to the hydrocarbonretaining system when temperature of the hydrocarbon retaining system isbelow a threshold value, the routing continuing until the hydrocarbonretaining system reaches a threshold purging temperature, and then routeexhaust gases to atmosphere, bypassing the hydrocarbon retaining system,and purge the hydrocarbon retaining system to the engine intake

As noted in FIG. 14, the control system may enable determination ofdegradation of the retaining system 22, such as to determine anddifferentiate degradation between a purge canister and an HC trap. Insome examples, the purge hydrocarbon concentration learned from exhaustgas oxygen sensor feedback and fuel injection adjustment may provideindependent estimates of the hydrocarbon storage, such as when a fueltank canister (e.g., 422) is at a different temperature than an HC trap(e.g., 310). Alternatively, the learned hydrocarbon amount duringpurging may be used to determine performance of an HC trap that wasloaded and then purged during condition with little to no fuel tankvapor generation, and before which the fuel tank vapors weresufficiently purged. In another particular example, the HC trap may bediagnosed based on detecting change in a temperature condition of gasduring purging of gases through the trap. Various examples, as well asadditional diagnostic approaches, are described below herein.

In the following examples, the diagnostics are described with respect tothe example of a carbon based hydrocarbon trap coupled in retainingsystem 22. Further, the operation is described in the example where,following a start up event, the exhaust flow is diverted through the HCtrap until the emission control device is sufficiently heated andreached a desired conversion efficiency. Further, following the storage,the trapped hydrocarbons are then purged by flowing air through the HCtrap back into the engine for combustion. The purge flow may be inseries or in parallel with the fuel tank generated evaporative emissionscarbon canister purge. However, the following diagnostics may also beapplied to various other system configurations and operating modes.

The following diagnostics may be applied as either or both of afunctional or threshold monitor. The functional monitor may determine ifa device is connected and functioning as expected while a thresholdmonitor may determine the effectiveness of the emission control device.

One potential degradation mode may include vibration and mechanicaldamage to carbon in the HC trap—e.g., carbon granules can be fracturedand worn down. As such, the HC trapping capability of the trap may bereduced if the carbon granules are broken down and potentially lost outthe tailpipe. If enough carbon is lost or compacted and the volume ofthe trap is no longer filled, some of the exhaust gas may bypass thecarbon bed and the tailpipe emissions can increase. Thus, one approachuses a monitor that detects a loss of carbon volume as a thresholdmonitor.

In a first approach, the control system may measure temperature at theoutlet of the HC trap during trapping and purging. Following a coldstart, it is expected that the temperature at the outlet will increaseas the exhaust system warms up. This indicates that the system isconnected to the exhaust system and the valves used to divert the flowto the trap are functioning. After the flow is allowed to bypass thetrap, the temperature should stabilize, indicating that the valves havecycled properly. A continued increase in the temperature would indicatethat the trap is still being exposed to exhaust gas. During the purgecycle, the temperature should drop as fresh air is inducted into thetrap.

In a second approach, pressure differential across the carbon bed of theHC trap may be measured during the trapping or purging as an indicationof the presence of a flow restriction due to the carbon. A loss ofcarbon would lead to a reduction in the pressure difference, for a givenflow rate. One or more pressure sensors may be mounted upstream and ordownstream of the HC trap.

In a third approach, a fuel vapor/hydrocarbon sensor may be used. Forexample, an HC sensor in the trap outlet may directly measure theeffectiveness of the trap during trapping since any degradation in thetrap would result in an increase in the HC breakthrough at vent 27. Somemodeling of the concentration and composition of the exhaust gas as afunction of speed/load/spark retard/temperatures and/or total fuelconsumed since start along with the expected reduction in pre-trap HCdue to catalyst light off may be used to improve the capability of athreshold monitor. Alternately, an empirical model of the expected HCout of the trap could be used.

In a fourth approach, temperature sensors placed before and after the HCtrap can provide an indication of a temperature difference during thetrapping (e.g., due to adsorption) and purging (e.g., desorption)phases. The temperature difference may also be affected by thepercentage of the flow that is adsorbed or desorbed on the carbon bed(primarily water and HC). In other examples, temperature deviations fromexpected or estimated values may be used. In the examples using an HCtrap in the exhaust system with a temperature sensor located downstream,the system may utilize an inferred exhaust temperature at the trapoutlet to generate a temperature difference between the inferred andactual temperature at the trap outlet. The system can then diagnoseadsorption function based on this temperature difference. Further, dueto potential errors in temperature estimates, identification of atemperature shift may be based on the initial temperature detected bythe temperature sensor, and then considering a measured temperature risein comparison to an estimated temperature rise during select conditions,such as storing or purging. Note also that in some examples, exhaust gasair-fuel ratio sensors may be operated as a temperature sensor underselect conditions.

In a fifth approach, a position measurement of the HC trap can be used.Specifically, to reduce vibration from damaging the carbon in the trapand/or canister, the devices may include a floating end plate and one ormore springs to maintain some level of pressure on the carbon. If thecarbon deteriorates in spite of these measures, the reduction in volumecan lead to a change in the position of the end plate(s) and a reductionin the force applied by the spring. Various methods to detect themovement may be used to identify the loss of carbon. In one example,these may include a position sensor, a thin wire that would break whenthe spring is extended, contacts that would open if the plate moves,transducers to measure the spring force, or strain gauge like devicesbuilt into the spring.

In a sixth approach, probes that measure the conductivity of the carbonbed may be used to provide an impedance measurement that would increasewith the loss of spring pressure or a reduction in the carbon volume.The resistance between two contact surfaces applied to the top of thecanister may show a larger increase if the bed settled enough to providea bypass path for the exhaust gasses. In one example, the conductivitymay be measured during select conditions, such as during warm-up, orafter warm-up.

Note that the example control and estimation routines included hereincan be used with various engine and/or vehicle system configurations.The specific routines described herein may represent one or more of anynumber of processing strategies such as event-driven, interrupt-driven,multi-tasking, multi-threading, and the like. As such, various acts,operations, or functions illustrated may be performed in the sequenceillustrated, in parallel, or in some cases omitted. Likewise, the orderof processing is not necessarily required to achieve the features andadvantages of the example embodiments described herein, but is providedfor ease of illustration and description. One or more of the illustratedacts or functions may be repeatedly performed depending on theparticular strategy being used. Further, the described acts maygraphically represent code to be programmed into the computer readablestorage medium in the engine control system.

It will be appreciated that the configurations and routines disclosedherein are exemplary in nature, and that these specific embodiments arenot to be considered in a limiting sense, because numerous variationsare possible. For example, the above technology can be applied to V-6,I-4, I-6, V-12, opposed 4, and other engine types. The subject matter ofthe present disclosure includes all novel and nonobvious combinationsand subcombinations of the various systems and configurations, and otherfeatures, functions, and/or properties disclosed herein.

The following claims particularly point out certain combinations andsubcombinations regarded as novel and nonobvious. These claims may referto “an” element or “a first” element or the equivalent thereof. Suchclaims should be understood to include incorporation of one or more suchelements, neither requiring nor excluding two or more such elements.Other combinations and subcombinations of the disclosed features,functions, elements, and/or properties may be claimed through amendmentof the present claims or through presentation of new claims in this or arelated application. Such claims, whether broader, narrower, equal, ordifferent in scope to the original claims, also are regarded as includedwithin the subject matter of the present disclosure.

The invention claimed is:
 1. A method for an engine comprising:selectively routing exhaust gases through a hydrocarbon retaining systemto store exhaust hydrocarbons; selectively purging stored hydrocarbonsfrom the hydrocarbon retaining system to an engine intake, the selectivepurging initiated responsive to an alcohol content of an injected fuel;and varying termination of the selective routing responsive to thealcohol content of the injected fuel by delaying the termination as thealcohol content increases.
 2. The method of claim 1, where theinitiation of the selective purging is further-responsive to an amountof hydrocarbons stored in the hydrocarbon retaining system.
 3. Themethod of claim 1, where the initiation of the selective purging isfurther responsive to exhaust temperature.
 4. The method of claim 1,where during the selective routing, exhaust gas enters the hydrocarbonretaining system via an inlet of the hydrocarbon retaining system andflows in a first direction through the hydrocarbon retaining system, theexhaust gas first entering a first hydrocarbon retaining device, andthen entering a second hydrocarbon retaining device of the hydrocarbonretaining system, serially; and where during the selective purging,purge gases enter the hydrocarbon retaining system via an outlet of thesystem and flow in a second, opposite direction through the hydrocarbonretaining system, the purge gases being routed in parallel through thefirst and second hydrocarbon retaining devices.
 5. The method of claim 1further comprising determining degradation of the hydrocarbon retainingsystem responsive to an exhaust air-fuel ratio sensor during thepurging.
 6. The method of claim 1, wherein initiating the selectivepurging responsive to the alcohol content of the injected fuel includes,as the alcohol content of the fuel increases, routing exhaust gases tostore exhaust hydrocarbons up to a higher storage amount and initiatingthe selective purging of the stored hydrocarbons at the higher storageamount.
 7. The method of claim 1, wherein initiating the selectivepurging responsive to the alcohol content of the injected fuel includes,as the alcohol content of the fuel increases, routing exhaust gases tostore exhaust hydrocarbons for a longer duration and initiating theselective purging of the stored hydrocarbons after the longer duration.8. The method of claim 1, wherein varying termination includes, when thealcohol content of the fuel is higher, one or more of continuing routingup to a higher storage amount and ending the routing at the higherstorage amount and continuing routing for a longer duration and endingthe routing after the longer duration.
 9. The method of claim 1, furthercomprising varying initiation of the selective purging by delaying theinitiation of the selective purging as the alcohol content of theinjected fuel increases.
 10. The method of claim 1, where the selectiverouting is performed during an engine start.
 11. The method of claim 10further comprising communicating the hydrocarbon retaining system with afuel tank to retain at least some fuel vapors from the tank in thehydrocarbon retaining system.
 12. The method of claim 10 furthercomprising adjusting fuel injection to the engine based on the selectivepurging to learn an amount of hydrocarbons stored in the hydrocarbonretaining system.
 13. The method of claim 10, wherein varyingtermination includes varying an ending of the routing to store exhausthydrocarbons at a higher temperature as the alcohol content increases.14. The method of claim 10 further comprising combusting a rich exhaustair-fuel ratio during at least a portion of the routing, even whentemperature of an emission control device is below a light-offtemperature, and further operating with exhaust air-fuel ratio aboutstoichiometry after an ending of the routing to store exhausthydrocarbons.
 15. The method of claim 10 further comprising transferringexhaust gas heat from the exhaust gas to fresh air drawn in to purge thehydrocarbon retaining system.
 16. A system for a vehicle including anengine having an intake and an exhaust, the system comprising: a fuelsystem of the vehicle; a hydrocarbon retaining system selectivelycoupled to the engine intake, engine exhaust, and fuel system; and acontroller with code for, selectively routing exhaust gases of theengine to the hydrocarbon retaining system to store exhausthydrocarbons; selectively routing fuel vapors from the fuel system tothe hydrocarbon retaining system; selectively purging storedhydrocarbons from the hydrocarbon retaining system to the engine intake;and varying an initiating of the selective purging and varying an endingof the routing to store exhaust hydrocarbons responsive to at least analcohol content of fuel combusted in the engine, the varying includingdelaying ending of hydrocarbon storage and delaying initiating ofhydrocarbon purging to higher exhaust temperatures as the alcoholcontent in the fuel increases.
 17. A system for a vehicle including anengine having an intake and an exhaust, the system comprising: a fuelsystem of the vehicle; a catalytic emission control device closelycoupled in the exhaust; a hydrocarbon retaining system selectivelycoupled to the engine intake, engine exhaust, and fuel system, thehydrocarbon retaining system having a vent positioned adjacent at leasta portion of the exhaust of the engine; and a controller for selectivelyrouting exhaust gases of the engine to the hydrocarbon retaining systemto store exhaust hydrocarbons; selectively routing fuel vapors from thefuel system to the hydrocarbon retaining system; selectively purgingstored hydrocarbons from the hydrocarbon retaining system to the engineintake by inducting fresh air into the vent; varying an initiating ofthe selective purging of stored hydrocarbons responsive to a temperatureof the emission control device; and varying an ending of the routing tostore exhaust hydrocarbons responsive to at least an alcohol content offuel combusted in the engine, wherein the controller includes furthercode for, as the alcohol content of the fuel increases, increasing atemperature threshold of exhaust gas routing through the hydrocarbonretaining system; routing exhaust gases to store exhaust hydrocarbons upto the increased temperature threshold; and initiating the selectivepurging at the increased temperature threshold.